The present application relates to a spacer for insertion between two vertebrae. In particular, the present application relates to a spacer with adjustable axial length which can be filled with bone graft after insertion between the vertebrae.
A spacer with adjustable axial length is known from U.S. Pat. No. 6,200,348. The spacer comprises a first sleeve-shaped member and a second member which is slidably guided within the first member for adjusting the overall length of the spacer. The adjustment of the axial length is made by means of ratchet notches provided at the outer wall of the second member and an engagement member provided at the first member. The spacer has a plurality of openings in its wall which allows insertion of bone cement and growing-in of blood vessels.
Usually the spacer is either filled with bone cement through infusion after insertion between the vertebrae or it is filled with bone material, in particular with bone graft, through the open ends of the tubular spacer before it is implanted into a patient's body. The length of the known spacer can be adjusted after the spacer is inserted between two vertebrae. In certain situations it is desirable to add or remove bone material to or from the interior of the spacer after adjusting the axial length of the spacer.
U.S. Pat. No. 6,616,695 B1 describes a spacer for insertion between two vertebrae the axial length of which can be adjusted. The spacer comprises a first tubular part having a threaded inner surface and a second tubular part having a threaded outer surface, said parts forming a screw-nut connection which allows adjustment of the axial length of the spacer. The first tubular part has a plurality of circular openings in its wall. The second tubular part has a plurality of elongate openings in its wall. The length of the spacer can be adjusted by turning the parts relative to each other. This requires more space than a sliding motion for adjusting the length. Furthermore, the vertebral body can be damaged by the toothed end plate of the spacer during the turning motion. The elongate openings serve for insertion of a fixing screw. The openings in the wall are too small for inserting bone graft.
U.S. Pat. No. 5,290,312 describes a prosthetic vertebra with adjustable axial length comprising a first hollow parallelepiped-shaped component and a second hollow parallelepiped-shaped component which can slide in the first component. Each component has an abutting end surface for abutting a vertebra and an anchoring window formed in the abutting end. Also, each component has an open first side which establishes an access window and an open end formed opposite the abutting end. The spacer comprises means for preventing slidable motion between the components to establish a desired length. To connect the spacer with the vertebrae, pliable bone cement is infused into the components through the access window which flows out of the anchor windows and hardens. Since each component has an open side, bone graft which would be inserted through this side can easily fall out. Furthermore, the open side leads to a reduced stability.
U.S. Pat. No. 6,524,341 B2 also discloses spacer with adjustable length. A turning motion is necessary for expansion and retraction of the parts of the spacer relative to each other.
U.S. Pat. No. 6,176,881 B1 discloses a spacer with adjustable length. The spacer comprises an interior hollow body and an exterior hollow body, the interior body has a catch mechanism on its outer surface and the exterior body includes an elastic element which latches onto the catch mechanism thereby fixing the length of the spacer in such a way that it is resistant to compression. If a blocking of the hollow bodies against expansion is desired, a locking screw is used which is arranged on one side of the spacer. If the length of the spacer shall be reduced again, the elastic element is actuated with a tool acting on the opposite side of the spacer. A spacer similar to that disclosed in U.S. Pat. No. 6,176,881 B1 is known under the trade name Synex. This spacer additionally has an access opening for introduction of bone graft. Based on the above, there is a need for a spacer for insertion between two vertebrae which can be adjusted in length and which can be filled in situ not only with bone cement but also with bone graft and which has an improved handling.